Sleeve filter centrifuge

ABSTRACT

A sleeve filter centrifuge comprises a drum with radial filtrate passages (12) which is rotatably mounted in a housing (1), a sleeve filter cloth (15) which covers the filtrate passages, a lid (18) which closes the front of the drum and has a filling opening for suspensions to be filtered, and a filling pipe (19) which penetrates the filling opening. In order to turn up the filter cloth, the drum and the lid can be displaced axially relative to each other by means of a hollow shaft (3) driven in rotation and a support shaft (9) which telescopes in and out of said hollow shaft. A threaded spindle (34) is arranged on the support shaft (9) and a nut (33,36) is engaged with the threaded spindle (34). Either the threaded spindle (34) or the nut (33,36) can be driven in rotation by a motor (44) in such a manner that the support shaft (9) telescopes in and out of the hollow shaft (3) in function of the rotational speed of the threaded spindle (34) or nut relative to the rotational speed of the hollow shaft (3).

The invention relates to a sleeve filter centrifuge according to thepreamble to patent claim 1.

In known sleeve filter centrifuges of this type (DE-PS 27 09 894) thesupport shaft, which is securely connected to the lid of the drum, istelescopically displaced back and forth in the hollow shaft bearing thedrum with the aid of a hydraulic drive when the drum is intended to beopened or closed by inverting the filter cloth. Since leakages cannot,in principle, be ruled out in the case of hydraulic drive means, eitherin the region of the actual drive cylinder or in the pipes leading tothis cylinder and the valves arranged therein, stoppages can, inprinciple, be caused hereby and these are extremely serious, inparticular, when filtering sensitive products, for examplepharmaceuticals, or in processes Carried out under sterile conditions.

The object of the invention is therefore to improve a sleeve filtercentrifuge of the generic type such that the hydraulic drive previouslyassociated with the opening and closing of the drum is dispensed withand, therefore, disruptive leakages of the hydraulic fluid are ruledout.

The following description of a preferred embodiment of the inventionserves to explain the invention in greater detail in conjunction withthe attached drawings. In these drawings,

FIG. 1 is a schematic side view of a sleeve filter centrifuge in theoperative phase of centrifugation;

FIG. 2 shows schematically the centrifuge of FIG. 1 in the operativephase of solids discharge;

FIG. 3 shows schematically an enlarged view of a mechanical drive meansfor opening and closing the drum of the sleeve filter centrifuge, and

FIG. 4 shows schematically an embodiment modified in comparison withFIG. 3.

The sleeve filter centrifuge illustrated in the drawings comprises ahousing 1 which is indicated schematically and hermetically encloses theentire machine. In this housing, a hollow shaft 3 is rotatably mountedin bearings 4, 5 on a stationary machine frame 2. The end of the hollowshaft 3 protruding beyond the bearing 5 is non-rotatably connected to adrive gear 6, via which the hollow shaft 3 is caused to rotate rapidlyby an electric or other motor 7 by means of a V belt.

The hollow shaft 3, which extends rigidly between the bearings 4, 5, hasan axially extending wedge-shaped groove which is indicated by brokenlines and in which a wedge-shaped member 8 is axially displaceable. Thiswedge-shaped member 8 is rigidly connected with a support shaft 9displaceable in the interior of the hollow shaft 3. The support shaft 9therefore rotates together with the hollow shaft 3 but is axiallydisplaceable therein.

The closed base of a bowl-shaped centrifugal drum 11 is flange-mountedin a non-rotatable manner on the end of the hollow shaft 3 located tothe left in FIGS. 1 and 2 and protruding beyond the bearing 4. The drum11 has radially extending through openings 12 in its cylindrical casing.The drum 11 is open at its end face opposite the base. The edge of afilter cloth 15 essentially circular cylindrical in design is sealinglyclamped by means of a holding ring 14 at the flange-like edge 13 of theopening surrounding this open end face. The other edge of the filtercloth 15 is sealingly connected in a corresponding manner to a baseportion 16 which is rigidly connected to the displaceable support shaft9 which penetrates freely through the base of the centrifugal drum 11.

A centrifugal chamber lid 18 is rigidly attached to the base portion 16via spacer bolts 17, leaving an intermediate space free. This lid, inFIG. 1, hermetically seals the centrifugal chamber of the drum 11 byengaging on the edge of its opening and, in FIG. 2, is lifted freelyaway from the drum 11, together with the base portion 16, by axialoutward displacement of the support shaft 9 out of the hollow shaft 3.

A feed pipe 19 is arranged at the front end of the sleeve filtercentrifuge located to the left in FIGS. 1 and 2. This pipe serves tosupply a suspension to the centrifugal chamber of the drum 11 which isto be separated into its solid and liquid components (FIG. 1) and in theoperative state illustrated in FIG. 2 the pipe penetrates into a bore 21of the displaceable support shaft 9.

The drive means, which brings about the displacement of the supportshaft 9 in the hollow shaft 3 and, therefore, the opening and closing ofthe centrifugal drum and, with it, the transition between the twooperative states illustrated in FIGS. 1 and 2, will be described lateron.

During operation, the sleeve filter centrifuge first takes up theposition shown in FIG. 1. The displaceable support shaft 9 is withdrawninto the hollow shaft 3, whereby the base portion 16 connected to thesupport shaft 9 is located in the vicinity of the base of thecentrifugal drum 11. The centrifugal chamber lid 16 hereby abutssealingly on the edge of the opening to the drum 11. When the drumrotates, suspension to be filtered is introduced via the feed pipe 19.The liquid components of the suspension pass through the openings 12 ofthe drum in the direction of the arrows 22 and are guided by a baffleplate 23 into a discharge line 24. The solid particles of the suspensionare retained by the filter cloth 15.

When the centrifugal drum 11 continues to rotate, the support shaft 9 isnow displaced (to the left) in accordance with Figure 2, whereby thefilter cloth 15 is turned outwards and the solid particles adheringthereto are catapulted outwards into the housing 1 in the direction ofthe arrows 25. From here they can easily be conveyed away. In theposition according to FIG. 2, the feed pipe 19 penetrates throughcorresponding openings in the lid 18 and in the base portion 16 into thebore 21 of the support shaft 9.

Once the solid particles have been thrown off under the influence of thecentrifugal force, the filter centrifuge is returned to the operativeposition according to FIG. 1 by moving the support shaft 9 back, thefilter cloth 15 hereby being turned back in the opposite direction. Inthis way, it is possible to operate the centrifuge with a constantlyrotating centrifugal drum 11; in the operative phase of centrifugationaccording to FIG. 1, the centrifugal drum 11 is driven by the motor 7 ata considerably greater rotational speed than in the operative state ofsolids discharge according to FIG. 2. In the latter operative phase thecentrifugal drum 11 rotates considerably more slowly.

As shown, in particular, in FIG. 3, a bushing 31 is rigidly andnon-rotatably flange-mounted at the end of the hollow shaft 3 supportedby the bearing 5 and this bushing projects rearwardly and has an axiallyextending slot 32. A nut 33 having a radially projecting wedge-shapedmember 30 is rigidly connected to the rear end of the support shaft 9.The wedge-shaped member engages in the wedge-shaped groove 32 so thatthe wedge-shaped member 30 provides a non-rotatable connection betweennut 33 and support shaft 9, on the one hand, and bushing 31 and hollowshaft 3, on the other, whereby the nut 33 and with it the support shaft9 are, however, axially displaceable in the bushing 31.

A screw spindle 34 having a corresponding external thread engages in theinternal thread of the nut 33 and is connected with a sleeve 36 via aconventional adjusting spring connection 35 so as to be non-rotatablebut slightly axially displaceable. The sleeve 36 is, for its part,rotatably mounted with the aid of bearings 37, 38 in an end piece 45rigidly flanged to the bushing 31. A disc 41 is held on the rearward endof the screw spindle 34 protruding beyond the sleeve 36 by means of anut 39. A cup spring 42 or the like is arranged between the rear endface of the sleeve 36 and the disc 41. This cup spring biases the screwspindle 34 relative to the sleeve 36 (towards the right in FIG. 3),whereby the adjusting spring connection 35 as mentioned between screwspindle 34 and sleeve 36 allows a slight axial movement between screwspindle 34 and sleeve 36.

A drive pulley 43 is non-rotatably seated on the sleeve 36 and isconnected via V belts with an additional electric or other motor 44(FIG. 1) which therefore rotatably drives the sleeve 36 and, with it,the screw spindle 34 non-rotatably connected therewith via the adjustingspring 35.

The cup spring 42, which biases the screw spindle 34 and, with it, thesupport shaft 9 as well via the nut 33 (to the right in FIG. 3), has thepurpose of holding the lid 18 in firm engagement on the edge of theopening of the centrifugal drum 11 during the operative phase ofcentrifugation (FIG. 1) and contrary to the hydraulic pressure occurringin the interior of the drum. In more simple embodiments of theinvention, the screw spindle 34 could also be rotatably mounted directlyin the bearings 37 and 38, i.e. without any intermediate sleeve 36. Inthis case, the drive pulley 43 would be seated directly on the screwspindle 34 and the cup spring 42 used for the specified purpose would beomitted.

As illustrated in addition, the bushing 31 is rotatably mounted in itsown pivot bearing 46 with the aid of the end piece 45 which is flangedto the bushing. This bearing is, for its part, supported on the machineframe 2 by a stand 47 so that the drive forces exerted by the drivepulley 43 and the motor 44 can be absorbed in the vicinity of thebearing 46.

When the screw spindle 34 is rotated via the drive pulley 43 and themotor 44 in one or other direction relative to the hollow shaft 3 andthe bushing 31 connected therewith, in which the screw spindle 34 isrotatably mounted, the support shaft 9 connected with the nut 33 isdisplaced in one or other direction due to the engagement of the screwspindle 34 in this nut so that the lid 18 connected to the support shaft9 performs the desired opening or closing movement.

During operation of the sleeve filter centrifuge, the hollow shaft 3bearing the centrifugal drum 11 and the bushing 31 rigidly connectedtherewith as well as the support shaft 9, which telescopes axially inthe hollow shaft 3 and is connected to the lid 18, do, however,constantly rotate in a predetermined direction of rotation. When the lid18 is opened and closed, it is, therefore, the relative speed of theseparts, i.e. in particular of the support shaft 9 and the screw spindle34, which is important and, above all, whether the screw spindle 34 isdriven at a lower or higher rotational speed than the support shaft 9.When support shaft 9 and screw spindle 34 have the same rotationalspeed, no axial displacement of the support shaft 9 in the hollow shaft3 takes place. Only when the rotational speed of the screw spindle 34 ishigher than the rotational speed of the support shaft 9 will this bedisplaced in the hollow shaft 3 in the sense of opening the lid 18. If,on the other hand, the rotational speed of the screw spindle 34 is lowerthan the rotational speed of the support shaft 9 or the screw spindle 34is driven in the opposite direction to the support shaft 9, the supportshaft, and with it the lid 18, will be displaced in the oppositedirection so that the lid 18 closes the centrifugal drum 11. In thepreferred embodiment of the invention, support shaft 9 and screw spindle34 always rotate in the same direction of rotation.

The hydraulic drive previously required for opening and closing thecentrifugal chamber drum is therefore replaced by a simple mechanicaldrive which no longer has the disadvantages with respect to leakage ofthe hydraulic drive. This is not, however, the only advantage of themechanical screw spindle drive as described. In contrast to thehydraulic drive, in which the support shaft 9 is displaced via ahydraulic cylinder flange-mounted at the rearward end of the hollowshaft 3, the forces required for opening and closing the drum as well askeeping the drum closed do not proceed via the main pivot bearings 4, 5but are absorbed internally by the screw spindle drive.

Since support shaft 9 and screw spindle 34 rotate, in the illustratedembodiment, simultaneously and in the same direction of rotation andwhen initiating an axial displacement of the support shaft 9 in thehollow shaft 3 only the difference in rotational speed between theseparts 9 and 34 in the positive and negative sense is important, only arelatively small axial stroke of the support shaft 9 is caused by arelatively high, absolute rotational speed of the screw spindle 34. Thescrew spindle 34 therefore acts in this respect as a screw having a veryslight pitch (fine thread) which, again, means that only slight forcesare required for its drive and, therefore, the motor 44 driving thescrew spindle 34 can be of a relatively low-powered design, and even inthe case where support shaft 9 and screw spindle 34 are driven inopposite directions of rotation.

At the end of the respective movement of stroke "opening" or "closing"the centrifugal drum, or even when the movement of stroke is ponderous,the difference in rotational speed between hollow shaft 3 and supportshaft 9, on the one hand, and screw spindle 34, on the other, is alteredtowards zero so that, finally, a synchronous rotation of these partstakes place. In this respect, an increase in force automatically occursand this has the effect, particularly after the closed state of thecentrifugal drum has been reached, that the centrifugal chamber lid 18is pressed firmly against the edge of the opening of the centrifugaldrum 11, even when the motor 44 driving the screw spindle 34 isrelatively low-powered.

As soon as the centrifugal drum 11 and, with it, the support shaft 9attempt to rotate more quickly than the screw spindle 34, thecentrifugal chamber lid 18 is automatically kept closed on thecentrifugal drum 11, even when the hydraulic forces effective in thecentrifugal chamber are greater. The screw spindle closure arrangementas described therefore acts like a screw spindle (provided with a finethread) with automatic locking which does not require any additionalradial locking. In particular, and in contrast to a hydraulic closurearrangement, the screw spindle closure arrangement as described does notrequire any additional safety device, such as, for example, acentrifugal governor or the like, which sees to it that it is possibleto open the centrifugal drum only below a predetermined rotational speedof the drum. In accordance with the invention, the centrifugal chamberlid 18 is always pressed automatically and securely onto the edge of theopening of the centrifugal drum 11 by the screw spindle drive asdescribed for as long as the screw spindle 34 rotates at a slower speedthan the support shaft 9 and the parts connected therewith or in theopposite direction thereto.

In FIG. 3, the open state of the centrifugal drum according to FIG. 2 isillustrated, in which the support shaft 9 is displaced by the screwspindle 34 right to the left in Figure 3. As illustrated, the supportshaft 9 has a hollow space 48 in front of the nut 3 connected with itand the screw spindle 34 enters this hollow space when the support shaftis brought back (to the right in FIG. 3) during the course of theclosing movement of the centrifugal drum. In this respect, the nut 33 isdisplaced accordingly in the bushing 31 forming a rearward extension ofthe hollow shaft 3.

In one embodiment of the invention which is not illustrated, the screwspindle can be a spindle without automatic locking which can, forexample, be realized by a conventional rotary ball spindle. In thiscase, the force required for keeping the centrifugal drum 11 securelyclosed is provided by the motor 44 which is constantly switched on anddrives the screw spindle 34 at a lower rotational speed than theelectromotor 7 the hollow shaft 3 and, with it, the support shaft 9. Itis also possible to have a separate, interconnectable brake acting onthe motor 44 or on a corresponding section of the screw spindle 34. Inthis case, the motor 44 itself can serve as a brake, in particular, whenthis motor is a frequency regulated electromotor.

Normally, the motor 44 does not initiate the opening movement of thecentrifugal drum 11 until it drives the screw spindle 34 at a higherrotational speed than that at which the centrifugal chamber drum and,with it, the support shaft 9 are rotating. When, therefore, the motor 44is driven at a constant speed during the operative phase ofcentrifugation (FIG. 1), it causes the drum to be kept firmly closed foras long as its speed is higher than the rotational speed of the screwspindle 34. The opening movement of the centrifugal drum will not takeplace until the rotational speed of the centrifugal drum 11 falls belowthe rotational speed of the screw spindle 34 during transition into theoperative phase of solids discharge (FIG. 2).

It is, in addition, possible to switch off the motor 44 driving thescrew spindle 34 completely once the closed or opened state of the drumhas been reached. Due to the automatic locking of the screw spindle 34in the nut 33, the screw spindle 34 and, with it the motor 44, is thentaken along during idling by the hollow shaft 3 driven by the motor 7.

FIG. 4 shows a further modified embodiment of the invention. In FIG. 4,parts corresponding to one another have been given the same referencenumerals as in FIGS. 1 to 3. Whereas in the embodiment according to FIG.3 the screw spindle 34 is rotatably driven via the drive pulley 43 andthe motor 44 in order to displace the support shaft 9 in the hollowshaft 3, in the embodiment according to FIG. 4 the screw spindle 34 isnon-rotatably connected with the support shaft 9 and the sleeve 36designed as a nut has an internal thread which engages with the externalthread of the screw spindle 34. The sleeve 36 is mounted in the endpiece 45 so as to be axially non-displaceable and is caused to rotatevia the drive pulley 43 and the motor 44 so that the screw spindle 34and, with it, the support shaft 9 are displaced axially back and forth,whereby the centrifugal chamber lid 18 is opened or closed in the manneralready described.

As illustrated in FIG. 4, the screw spindle 34 is mounted via anadjusting spring 35 in a part 33 so as to be slidingly displaceable inaxial direction. This part is, for its part, rigidly connected to thesupport shaft 9. In this way, the screw spindle 34 is non-rotatablyconnected to the support shaft 9 but can be axially displaced relativethereto over a limited distance. In the interior of the support shaft 9,the disc 41 is held by the nut 39 and one end of the cup spring 42 issupported on this disc. The other end of the cup spring 42 abuts in thehollow space 48 of the support shaft 9 on an inner shoulder 49 or thelike so that the cup spring 42 attempts, as in the embodiment accordingto FIG. 3, to bias the support shaft 9 such that in the operative phaseof centrifugation (FIG. 1) the centrifugal chamber lid 18 is held infirm engagement on the edge of the opening of the centrifugal drum 11.

The embodiment according to FIG. 4 represents to a certain extent a"kinematical inversion" in comparison with the embodiment according toFIG. 3. The two embodiments correspond to one another in theirfunctioning and advantages.

In a further embodiment (not illustrated) of the inventive "screwclosure" of drum 11 and lid 16, the sleeve 36 which acts in FIG. 4 as arotatably driven nut could also be arranged between the stationarymachine frame 2 (cf. FIG. 1) and the drum 11 if the support shaft 9exiting from the hollow shaft 3 is provided at this point with acorresponding external thread which engages with the sleeve acting as anut. In this case, as well, the sleeve would be driven via a drivepulley 43 and a motor 44 arranged accordingly.

I claim:
 1. Sleeve filter centrifuge comprising a drum (11) rotatablymounted in a housing (1) and having radial filtrate passages (12), aninvertable filter cloth (15) covering the filtrate passages, a lid (18)closing one end face of the drum, a feed opening provided in the lid forthe suspension to be filtered and a feed pipe (19) passing through thefeed opening, drum and lid being axially displaceable relative to oneanother by means of a rotatably driven hollow shaft (3) and a supportshaft (9) telescopically reciprocating therein in order to invert thefilter cloth, a screw spindle (34) is arranged on the support shaft (9)and a nut (33, 36) engaging with this screw spindle is provided, andthat either the screw spindle (34) or the nut (36) is rotatinglydrivable by a motor (44) so that the support shaft (9) reciprocatestelescopically in the hollow shaft (3) in response to the rotationalspeed of the screw spindle (34) or the nut (36) relative to therotational speed of the hollow shaft (3).
 2. Sleeve filter centrifuge asdefined in claim 1, in which the nut (33) is securely arranged on therear end of the support shaft (9) remote from the drum (11) and thescrew spindle (34) engages in the nut, the screw spindle (34) isrotatably mounted in a rearward extension (bushing 31) of the hollowshaft (3) directed away from the drum (11), and the screw spindle (34)is rotatingly drivable via the motor (44).
 3. Sleeve filter centrifugeas defined in claim 2, in which the support shaft (9) has a hollow space(48) between the drum (11) and the nut 33, a free end of the screwspindle (34) penetrating into the hollow space when the support shaft(9) is displaced accordingly relative to the hollow shaft (3).
 4. Sleevefilter cartridge as defined in claim 2 in which an axially parallelrecess (32) is provided at a rearward extension (bushing 31) of thehollow shaft (3), a wedge-shaped member (30) rigidly connected to thesupport shaft (9) engaging in this recess to secure the shaft againstrotation and in that the wedge-shaped member (30) is arranged on the nut(33).
 5. Sleeve filter cartridge as defined in claim 2 in which anaxially parallel recess (32) is provided at a rearward extension(bushing 31) of the hollow shaft (3), a wedge-shaped member (30) rigidlyconnected to the support shaft (9) engaging in this recess to secure theshaft against rotation and in that the screw spindle (34) is arranged ina sleeve (36) rotatable in the rearward extension (bushing 31) of thehollow shaft (3) so as to be non-rotatable and slidingly displaceable,and the sleeve (36) is drivable via the motor (44).
 6. Sleeve filtercentrifuge as defined in claim 5, in which the screw spindle (34)projects freely beyond the sleeve (36) at its rear end remote from thesupport shaft (9) and a spring (42) is arranged between this rear end ofthe sleeve (36) and the free end of the screw spindle (34), the springbiasing the screw spindle (34) and with it the support shaft (9) towardsthe sleeve (36).
 7. Sleeve filter centrifuge as defined in claim 1, inwhich the screw spindle (34) is non-rotatably connected with the supportshaft (9) and a rotatable and axially non-displaceable nut (36)rotatably drivable via the motor (44) engages the external thread of thescrew spindle.
 8. Sleeve filter centrifuge as defined in claim 1, inwhich an axially parallel recess (32) is provided at a rearwardextension (bushing 31) of the hollow shaft (3), a wedge-shaped member(30) rigidly connected to the support shaft (9) engaging in this recessto secure the shaft against rotation.
 9. Sleeve filter centrifuge asdefined in claim 8, in which the rearward extension (bushing 31) of thehollow shaft (3) is supported in at least one pivot bearing (46, 47).10. Sleeve filter centrifuge as defined in claim 1, in which the screwspindle (34) is drivable by the motor (44) via a drive pulley (43).